The dimension of a device is getting smaller as the semiconductor technology is getting developed. When the level of integration of ICs is increased, the surface area of the chip is not sufficient to fabricate the required interconnections in a single layer, so that a design including more than two layers of metal interconnections is adopted in the VLSI technology. The dual damascene process is a widely used metal interconnection technology due to the advantages of improving the device reliability and increasing the production.
The dual damascene process includes forming a dual damascene opening and filling a metal in the dual damascene opening. Generally speaking, a lot of resides form during the process of etching the dual damascene opening. Thus, a cleaning process is performed before the step of filling the metal in the dual damascene opening. Hydrofluoric acid (HF) is usually used as a cleaning solution in the cleaning process. However, when the titanium nitride (TiN) hard mask layer is applied in the dual damascene process, the HF cleaning solution cannot remove the residues effectively and is easy to cause the copper loss in the copper layer exposed by the dual damascene opening; thus, the device feature of the copper layer is affected and the yield of the product is reduced.